Polyethylene terephthalate (PET) is a kind of polymer with excellent performance. PET is preferred for its high modulus, high strength, crispness, good shape retention, pure hygiene and good barrier property. Thus, it is widely used in fiber, bottle packaging, film and sheet and other fields. The output increases year by year, and the status of the industry is significantly improved.
PET is a symmetrical linear macromolecule, the molecular chain does not contain side chain groups, regularity is very good, this structure has a high glass transition temperature, so it needs to dye at high temperatures, in order to promote the dye molecules to the fiber interior the proliferation. In addition. PET molecular chain regular, good crystallinity, molecular chains arranged closely, and the molecular chain does not have molecules polar groups to react with dye molecules, so that it is more difficult to color polyester fiber. Because of its lack of hydrophilic groups in the molecule, its hygroscopicity is poor, which results difficulties in dying dacron. Polyester disperse dyeing mainly uses high-temperature high-pressure dyeing method.
Oligomers in polyester fibers are low molecular weight esters or ethers that primarily refers to oligomers with a degree of polymerization of less than 10. Diethylene glycol is produced as a by-product. Among them, oligomers are divided into linear oligomers and cyclic oligomers, of which cyclic polymers, especially cyclic trimers are the main part. Oligomers are mainly involved in heterogeneous nucleation, spinning processing, dyeing and the like. Polyester performance and after processing are adversely affected by oligomer. Ethylene terephthalate polymers (PET) contain about 3-4% of oligomers, and the presence of oligomers on the fiber surface can cause problems with dyeing and finishing. Diffusion of oligomers is most likely to occur during temperature control and incubation of the dye. When cooling, the same as the dye, the solubility of the oligomer in water decreases drastically with decreasing temperature and thus crystallizes out. The precipitated dye and oligomer adhere to the surface of the fiber and are very difficult to wash off, bringing a lot of trouble to dyeing and finishing. During dyeing process, the accumulation of dyes and oligomers adhered to the fiber surface, causing dye color spots, stains, color flowers and so on. Deposition in the dyeing machine pipes and valves, impede the flow of liquid, resulting in dyeing difficulties. The key to elimination of the oligomers is to eliminate the oligomer cyclic trimer and diethylene glycol, on the one hand to reduce oligomer production during the polymerization and on the other hand to remove them before or during dyeing.
Hetero-shrinking composite yarn is a kind of filament with different potential shrinkage properties, that is, high-shrinkage partially oriented yarn (POY) and low-shrinkage fully drawn yarn (FDY) are mixed fiber. The main features of PET different-shrinkage composite yarn are high bulkiness and softness. The appearance of PET different shrinkage composite silk is similar to ordinary filaments. Filaments with different potential shrinkage properties, that is, composite yarns composed of high-shrinkage POY and low-shrinkage FDY, are produced by mixed fiber processing. The shrinkage of the two components causes different shrinkage.